| Tunable dual-frequency lasers with large frequency difference have great application potential in the fields of laser interferometry,optically generated millimeter waves,and lidar.The commonly used dual-frequency laser generation methods mainly use the Zeeman effect,the Sagnac effect,the magneto-optical effect,the optical rotation effect and the birefringence effect,etc.,to split a laser frequency to obtain two frequencies.The 0.632μm dual-frequency He-Ne laser based on the Zeeman effect is limited by the fluorescence linewidth of Ne atoms（1500 MHz）,and the frequency splitting amount is small.In comparison,the solid-state fluorescence linewidth is much larger than that of gas,and the solid-state laser that obtains dual-frequency lasers by introducing birefringence effect is easier to achieve the purpose of increasing the frequency difference.Therefore,it is of great scientific value to carry out research on dual-frequency solid-state laser technology with large frequency difference,tunable frequency difference,and high power.The main contents of this dissertation are as follows:First of all,The development status and trends of dual-frequency laser technology at home and abroad are introduced.Further,based on the principle of laser theory,the relevant properties of neodymium ions are introduced,and their physical and optical properties as well as laser properties are discussed.The commonly used laser single longitudinal The mode selection method and technical characteristics are discussed.The method and principle of frequency splitting by birefringence effect are discussed.Secondly,the laser diode（LD）-pumped 1064 nm twisted-mode structure dual-frequency Nd:YAG laser is designed.Placeλ/4 waveplates at both ends of the Nd:YAG laser crystal.One of theλ/4 waveplates is fixed and the otherλ/4 waveplate is rotated.The relationship between the frequency splitting amount and the angle of the wave plate of the torsional mode dual-frequency laser is theoretically analyzed.The output characteristics,mode selection characteristics,longitudinal mode splitting characteristics,polarization characteristics and beam quality of the twisted-mode dual-frequency Nd:YAG laser are experimentally studied.The experimental results show that when the twoλ/4 waveplates are orthogonal,the laser is in a single longitudinal mode output state.By changing the angle between the two waveplates,the single longitudinal mode is split,and the two split modes are mutually orthogonal.Linearly polarized mode.Finally,a dual-frequency laser with adjustable frequency difference was obtained,with a maximum frequency difference of 2.3GHz（half of the free spectral range）.The experimental results are consistent with the theoretical analysis.The maximum output power is 50.9 m W.The M2 factors of the laser in the X and Y directions are respectively are 1.180 and 1.177,and the beam quality is good.Thirdly,the optical circuit composition of the ytterbium-doped(Yb3+)fiber amplifier system is introduced,and the output characteristics of the amplifier are simulated.The double-frequency Nd:YAG laser with a twisted mode structure is used as the seed source,and the ytterbium(Yb3+)fiber amplifier is used for power amplification.experiment.The seed optical power in the experiment is 35 m W,and the frequency splitting amounts are 0.4GHz,0.6 GHz,and 1.2 GHz,respectively,which are coupled into the single-mode polarization-maintaining fiber with an efficiency of 48%,and the power after connecting to the fiber amplifier is about 15 m W.The results show that the frequency difference after amplification and the frequency difference of the injected seed light do not change significantly for the dual-frequency laser under different amplification powers.Finally,a dual-frequency laser with an output power of 10 W was realized,and the M2 factors of the amplified beam quality in the X and Y directions were 1.211 and 1.257,respectively. |
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